JP2005112475A - Manufacturing method for synthetic resin pallet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method for a synthetic resin pallet that a multilayer injection can be performed by using a one-point gate system and a recycled plastic material is intended not to appear on a surface layer (skin layer). <P>SOLUTION: The manufacturing method of the synthetic resin pallet consisting of a deck board and beams and having at least a part thereof comprising the skin layer, which is the surface layer and a core layer, which is an internal layer comprises the steps of providing a one gate section at almost the central section of the deck board, firstly injecting a skin layer resin, which is to the surface layer into the cavity of a mold from the gate section, and then injecting the core layer resin, which is to be the internal layer slightly later, thereby forming the skin layer, which is the surface layer and the core layer, which is the internal layer. In the manufacturing method, it is preferable that a round rib is provided on the lower surface at almost the central section of a panel where the gate section is present and a runner rib where the panel is thicker formed than other portions is provided in the scope of the round rib. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a synthetic resin pallet for forklifts used when storing and transporting cargo, and more specifically, manufacturing a synthetic resin pallet in which at least a part of the pallet has a two-layer structure of a surface layer and an inner layer. Regarding the method.

  Conventionally, many pallets for storing and transporting luggage have been made of synthetic resin pallets that are excellent in water resistance and corrosion resistance in place of wooden pallets. Since the synthetic resin pallet is a large injection molded product, the dimensional accuracy, strength, etc. of the product are affected by conditions such as the dividing surface of the mold, the runner, and the gate. In particular, since this kind of pallet is a large product such as 1000 mm × 1000 mm, 1100 mm × 1200 mm, it is usually injection-molded with four or more gates. The reason for using the multi-point gate system with a large number of gates in this way is to secure the fluidity of the resin during injection molding and complete the solidification in a short time to increase the productivity. Further, in the foamed resin molded product, the difference in the foam density of each part increases as the resin flow distance becomes longer than the gate part.

  On the other hand, in recent years, with the increasing awareness of protecting the natural environment, the movement of recycling plastic products has become stronger. These plastic products can be repeatedly recycled and used, and recycled plastic materials are used in many fields. However, since the recycled plastic material is already colored, there is a problem that it is difficult to use it alone.

  Further, in the conventional synthetic resin pallet, in order to reduce the cost, the discarded resin product is reused, and at that time, a certain percentage of recycled plastic material is mixed with the virgin material and molded.

  However, the use of recycled plastic materials has the following problems. For example, beer makers and liquor makers use palettes based on their own image colors, and different color palettes from different companies are used in the distribution of products such as beer. Therefore, it is difficult for a distributor to efficiently collect a waste pallet such as a damaged pallet for each manufacturer.

  Also, a recycled plastic material in which a plurality of colors are mixed cannot be used as it is, unlike an image color. Therefore, in order to use the recycled plastic material, it is necessary to prepare a large amount of expensive pigments, which not only makes it difficult to adjust the color of the molded product, but also increases the cost.

  Furthermore, the conventional molding method uses a multi-point gate method, and increasing the number of gates increases the generation of welds. In the weld section, when the flow of resin splits and meets again, the tip of the fluidized resin cools and oxidizes, making it impossible to completely merge, and the air in the cavity and resin volatiles merge. It occurs to prevent it and is found in most injection-molded products.

  As a countermeasure against defects in the welded portion, the fluidity of the resin is improved. For this reason, in a large molded product such as a pallet, the number of gates is set to a multipoint gate method so as to increase the filling speed. However, adopting the multipoint gate system does not prevent the occurrence of welds even if measures are taken to improve the fluidity of the resin.

  The present invention has been made in view of the present situation, and provides a method of manufacturing a synthetic resin pallet that enables multilayer injection using a one-point gate method so that the use of recycled plastic material does not appear on the surface layer (skin layer). The purpose is to provide.

  In order to achieve the above object, the present invention is configured as follows. That is, the method for producing a synthetic resin pallet according to the present invention is a method for producing a synthetic resin pallet comprising a deck board and a girder and having at least a skin layer as a surface layer and a core layer as an inner layer. The deck board is provided with a single gate part in the center of the deck board, and the skin layer resin as the surface layer is first injected into the cavity of the mold from the gate part, and then the core layer resin as the inner layer with a slight delay. Is formed into a skin layer as a surface layer and a core layer as an inner layer. In the manufacturing method, a circular rib is provided on the lower surface of the top plate with the gate portion as a center, and the thickness of the top plate in the range within the circular rib is formed to be thicker than other portions, so that the resin flow is improved. It is preferable to function as a runner rib.

  The core layer is preferably molded from a polyolefin resin material having a flexural modulus of 1000 MPa to 5000 MPa. By using such a material, it is possible to manufacture a pallet that is lightweight, has high bending strength, and is inexpensive. The core layer is preferably 10 to 70% by weight of the entire pallet. Alternatively, the skin layer may be a non-foamed body, and the core layer may be molded from a foamed resin material having an expansion ratio of 1.05 to 1.5.

  In the case of molding by the one-point gate method, the number of welds is only the four corners of the deck board, and the resin amount of the core layer can be sufficiently filled. Further, in the above manufacturing method, by using a one-point gate system in which the gate portion is provided with a single gate portion in the substantially central portion of the deck board, the resin flows at almost the same speed as a whole, and the gas in the mold Can be uniformly removed from the entire mold, so that the occurrence of welds can be prevented. Then, by using a one-point gate system, a circular rib is provided on the lower surface of the top plate with the gate portion as the center, and the thickness of the top plate in the range of the circular rib is formed to be thicker than other portions, thereby allowing the resin flow. Becomes even smoother.

  With the single-point gate method, the molten resin that becomes the skin layer and the molten resin that becomes the core layer flow in a uniform flow rate in two layers, so the skin layer and the core layer can be formed even in relatively thin portions. Can do. Further, by molding the core layer with a material having a high bending elastic modulus, for example, a polyolefin resin material having a bending elastic modulus of 1000 MPa to 5000 MPa, a light and high bending strength pallet can be manufactured. In addition, since the core layer is 10 to 70% by weight of the entire pallet, the cost is reduced by the two-layer structure, the skin layer is broken and the core layer is exposed, or the skin layer and the core layer are mixed in the weld portion. There is no fear of

  In addition, since a two-layer structure including a skin layer and a core layer is used, an inexpensive recycled plastic material can be used for the core layer, and a material having aesthetics, conductivity, weather resistance, or the like can be used for the skin layer. And since the recycled plastic material which mixed and pulverized the waste product collected indiscriminately can be used for the recycled plastic material of a core layer, a recycled plastic material can be used effectively. Further, by using an image color material for the skin layer and a recycled plastic material for the core layer, the image color can be continuously maintained. In addition, by forming the skin layer from a non-foamed resin, the surface can be smoothed, a pallet that is difficult to get dirty can be obtained, and even if it becomes dirty, the stain can be easily removed.

  Embodiments illustrating the present invention will be described in detail below. First, FIG.1 and FIG.2 shows an example of the pallet manufactured by this invention. The synthetic resin pallet 10 is a four-way pallet, and is formed by welding two parts of an upper molded member 11 and a lower molded member 13 which are separately separately molded in advance. The upper molding member 11 includes an upper deck board 15 and girders 17a to 17c, and the lower molding member 13 includes a lower deck board 19 and girders 20a to 20c. The end surfaces of the girders 17a to 17c and the girders 20a to 20c are abutted. Molded by welding.

  The girders 17a to 17c and the girders 20a to 20c are hollow structures, respectively, and the girders 17a and 20a at the four corners of the deck board, the girders 17b and 20b at the middle part thereof, and the central girders 17c located at the diagonal intersections, respectively. 20c. A space surrounded by the beams 17a to 17b, beams 20a to 20b, the upper deck board 15, and the lower deck board 19 is used as a fork insertion port 21.

  The resin used for the synthetic resin pallet 10 may be a polyolefin-based resin such as polyethylene or polypropylene, and one or more of a foaming agent, conductive filler, glass fiber, weathering chemical, pigment, etc., if necessary. Two or more may be added.

  In the present invention, the lower deck board 19 may have the same configuration as that of the upper deck board 15, but the portion surrounded by the inner front end portion of the beam may be used as the opening surface. Therefore, the structure of the pallet described below may be provided at least on the upper deck board 15. The upper deck board 15 includes a top plate 23 and reinforcing ribs 25 provided vertically and horizontally on the lower surface of the top plate 23, and the overall height is determined by the height dimension of the reinforcing rib 25. A through hole 27 is formed at an appropriate position on the top plate 23 surrounded by the reinforcing rib 25.

  Further, among the reinforcing ribs 25, the reinforcing ribs 25a and 25b for connecting the corners of the four-spar spar 17a and the corners of the middle spar 17b, the corners of the middle spar 17b, and the corners of the central spar 17c. Further, the reinforcing rib 25c that connects the two, and the reinforcing rib 25d provided substantially at the center between the girders are relatively thicker than the other reinforcing ribs.

  The gate portion 30 is provided at a substantially central portion of the top plate 23, and a circular rib 31 centering on the gate portion is provided on the lower surface of the top plate 23 on the opposite side of the gate portion 30. Reinforcing ribs 33 are provided from the circular ribs 31 so as to be connected to the corners of the central portion 17c. The reinforcing rib 33 functions as a runner rib that improves the flow of resin during injection molding and allows the resin to flow smoothly. The formation of the circular ribs 31 is to prevent the reinforcing ribs 33 from crossing each other, resulting in a thickened portion at the intersection, which takes time for cooling and uneven shrinkage.

  Further, in order to ensure the fluidity of the resin, the thickness N of the top plate 23a in the circular rib 31 is formed to be thicker than the thickness N1 of other portions of the top plate. By forming the thickness N of the top plate 23a thick, the flow resistance of the resin can be reduced in combination with the provision of the reinforcing ribs 33. As in this embodiment, the single-point gate method is particularly effective when the internal structure is a two-layer structure described below.

  Next, the internal structure of the top plate and the reinforcing rib, which is a feature of the present invention, will be described. 3 and 4 are enlarged views of a cross section of the main part. The top plate 23 and the reinforcing ribs 25 have a two-layer structure of a skin layer S as a surface layer and a core layer K as an inner layer, and are molded by two types of resins.

  Next, a method for manufacturing the pallet having the two-layer structure will be described. First, a resin for forming the skin layer S is first injected into the mold from one gate portion, and then a resin for forming the core layer K is injected into the mold with a slight delay. Thus, by providing a time difference in the injection of the skin layer S and the core layer K, a two-layer structure in which the core layer K is covered with the skin layer S can be obtained.

  When the resin for forming the skin layer S is injected and the resin for forming the core layer K is injected later, the resin forming the skin layer is solidified on the wall surface of the mold cavity while flowing in two layers. Then, the resin forming the core layer K is confined to form the core layer. In order to solve the problem that the core layer protrudes into the skin layer or the core layer and the skin layer are mixed, the resin of the core layer K is immediately before the resin injected from the gate portion hits the tip of the cavity. The amount of resin, molding conditions, etc. are adjusted so that the injection is completed.

  The two-layer structure of the skin layer S and the core layer K is preferably formed on the entire pallet. However, since the skin layer S is solidified before the core layer K is filled in the thin portion or the like, the core layer Layers are difficult to form. Among the reinforcing ribs 25, the reinforcing ribs 25a and 25b, the reinforcing rib 25c, and the reinforcing rib 25d are formed relatively thicker than the other reinforcing ribs. It is formed in a two-layer structure consisting of K.

  The core layer K may be 10 to 70% by weight although it depends on the structure and size of the reinforcing rib. If the core layer is less than 10% by weight, the cost can not be reduced by the two-layer structure. If it exceeds 70% by weight, the skin layer may be broken to expose the core layer, or the skin layer and the core layer may be mixed in the weld portion. The material used for the core layer K is not particularly limited as long as it is a resin compatible with the skin layer. For example, various recycled plastic materials of polyolefin resin can be used. Moreover, it does not ask | require whether it is a foamed resin if it is a non-foamed resin, but in order to use a foamed resin, it is preferable that expansion ratio is 1.05-1.5.

  Further, by molding the core layer K with a material having a high bending elastic modulus, for example, a polyolefin resin material having a bending elastic modulus of 1000 MPa to 5000 MPa, a light and high bending strength pallet can be manufactured. Since the core layer K is covered with the skin layer S in a sandwich shape, a recycled plastic material can be used. Recycled plastic materials can be injection-molded resins such as those mixed with printing ink, vulcanized rubber powder, wood powder, paper powder, other fibers, or filled resin such as calcium carbonate. There may be.

For the skin layer S, a resin having conductivity or a resin having weather resistance in addition to conductivity can be used. Moreover, it does not ask | require whether the skin layer S is a foamed resin if it is a non-foamed resin. When the skin layer is formed of a non-foamed resin, the surface can be smoothed, a pallet that is difficult to get dirty can be obtained, and even when it is dirty, the stain can be easily removed.
In addition, by improving the weather resistance of only the skin layer or making it a desired color, the amount of weathering chemicals, pigments, etc. used can be reduced, and the cost can be reduced.

  The reinforcing ribs provided on the lower surface of the top plate 23 are not limited to the grid-like ribs parallel to the end face of the pallet, but may be ribs provided obliquely on the end face of the pallet, or a combination of these. May be. Moreover, in order to improve the flow of the resin from the gate part 30 at the central part to the girder 17a at the four corners, a runner rib connecting the gate part 30 and the girder 17a may be provided. In the above embodiment, the four-way pallet has been described. However, the present invention is not limited to the four-way pallet, and a two-way pallet can be applied as appropriate.

It is a front view which shows an example of the pallet which concerns on this invention. The right half is a plan view of the pallet, and the left half is a cross-sectional view taken along line AA of FIG. It is the BB sectional view taken on the line in FIG. It is CC sectional view taken on the line in FIG. It is principal part sectional drawing in a gate part.

Explanation of symbols

10 Four-way pallet
11 Upper molding member 13 Lower molding member
15 Upper deck board 17a-17c Girder
19 Lower deck board 20a-20c digit
23 Top plate
25 Reinforcing ribs 25a, 25b, 25c, 25d Thick reinforcing ribs 30 Gate portion
31 Circular rib 33 Reinforcing rib

Claims (5)

  A synthetic resin pallet manufacturing method comprising a deck board and girders, at least part of which is a skin layer that is a surface layer and a core layer that is an inner layer, and is provided with a single gate portion at substantially the center of the deck board, By injecting the resin of the skin layer as the surface layer into the mold cavity first from the gate portion, and then injecting the resin of the core layer as the inner layer with a slight delay, the skin layer and the inner layer as the surface layer A method for producing a synthetic resin pallet for molding a core layer.   A circular rib is provided on the lower surface of the top plate with the gate portion at the center, and the thickness of the top plate in the range within the circular rib is formed to be thicker than other portions, so that it functions as a runner rib that improves the flow of resin. Item 2. A method for producing a synthetic resin pallet according to Item 1.   The method for producing a synthetic resin pallet according to claim 1 or 2, wherein the core layer is molded from a polyolefin resin material having a flexural modulus of 1000 MPa to 5000 MPa.   The method for producing a synthetic resin pallet according to claim 1 or 2, wherein the core layer is injected so as to be 10 to 70% by weight of the whole pallet.   The method for producing a synthetic resin pallet according to claim 1 or 2, wherein the skin layer is a non-foamed body and the core layer is a foamed body having a foaming ratio of 1.05 to 1.5.

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